Ordered a sido 3" inlet 2.5" outlet super 10 series flow. Turns out I should have ordered a 2.5" inlet 2.25" outlet. The guy at the muffler shop said I had 2.5" pipe coming in, and 2.25" out (currently have a sido setup, just swapping mufflers). Does it matter? Will it sound different?

Trying to decide if I should exchange for the correct model, or if I should just have a shop use reducers to make it fit...it will be getting welded regardless. I checked flowmaster's site and the outside dimensions are the same size regardless of inlet/outlet size, which makes me think the guts are the same...